CMB foreground modeling and its subtraction:

a prospect from galaxy evolution

Cosmic Microwave Background Radiation and Its Foreground Interstellar Components, Tokyo, 17th February, 2010

Tsutomu T. TAKEUCHIInstitute for Advanced Research, Nagoya University, Japan

Galaxy meets cosmology again

Hinshaw et al. (2007)

1. CMB and Foregrounds1.1 Schematic view of the CMB foregrounds

1.2 Foregrounds from the CMB point of view

Galactic disk

Foregrounds: • Galactic: in the Milky Way,• Extragalactic: at a cosmological distance.

1.2 Foregrounds from the CMB point of viewForegrounds: • Galactic: strongly anisotropic,• Extragalactic: (supposedly) isotropic.

Galactic disk

Galactic: astrophysical approach (with local statistics)e.g., multiwavelength map-based subtraction.

Extragalactic: global statistical approache.g., power spectrum (Cℓ)-based treatment.

1.2 Foregrounds from the CMB point of viewForegrounds: • Galactic: strongly anisotropic,• Extragalactic: (supposedly) isotropic.

Galactic: astrophysical approach (with local statistics)e.g., multiwavelength map-based subtraction.

Extragalactic: global statistical approache.g., power spectrum (Cℓ)-based treatment.

1.2 Foregrounds from the CMB point of viewForegrounds: • Galactic: strongly anisotropic,• Extragalactic: (supposedly) isotropic.

Though the approach would be different, both of them are basically based on galaxies (including our Galaxy). Then, common knowledge can be used.

Galaxies contributing to the radio are divided into two categories:1. Star forming galaxies2. AGNs

2. Extragalactic Foregrounds2.1 Dusty galaxies as a contributor to the CMB

There are various cosmological sources of the CMB foreground, and especially dusty IR galaxies and radio galaxies are relevant.

Both can be treated simultaneously in the framework of phenomenological galaxy evolution model, since the physical origin of radio continuum is similar (thermal free-free and synchrotron radiation), and they are thought to be related physically (e.g., scenario of starburst-AGN connection).

Ingredients of the model

1. Spectral energy distribution (SED)

2. Luminosity function (LF)

3. Cosmological parameters

4. Galaxy Evolution (in principle, related to SEDs and LF)

Phenomenological dusty galaxy evolution model

Takeuchi et al. (2001a, b, 2002)Lagache et al. (2003, 2004)Le Borgne et al. (2008)Valiante et al. (2009)Béthermin et al. (2011)…

Dopita et al. (2005)

Current status of the SED modeling

As for radio galaxies, we can use the same framework with physical processes of accretion disk and jets. But they are rather minor contributors.

Empirical models try to constrain the evolution of galaxies by reproducing galaxy number counts, integrated background spectrum, and recently LF directly.

(Takeuchi et al. 2001a, Le Borgne et al. 2008, Valiante et al. 2009)

Constraints on the evolution from observation

Cosmic infrared background spectrum

Le Borgne et al. (2008)Takeuchi et al. (2001a)

To calculate the power spectrum of the fluctuation of the cosmic IR background (CIB), we need to model the clustering property of dusty galaxies, which is still very uncertain.

IR galaxy evolution with a halo model: Song et al. (2003) Takeuchi et al. (2005a) Amblard & Cooray (2007) Hall et al. (2010) Marsden et al. (2009)…

Since the connection between dark halo formation and galaxy formation is far from being well understood, we need to introduce a simplistic model. Currently the most popular one is the halo model, but still quite premature.

2.2 Evolution of the clustering of IR galaxies

Pénin et al. (2011)

1. Large scale: statistically characterized by the correlation of virialized structures (halos).

2. Small scale: characterized by the internal density profile of each halo.

2pt-correlation functionHalo mass profile

Quasi nonlinear

Nonlinear

Basic idea of the halo model

Then, the nonlinear power spectrum of the matter/galaxy distribution is described by halo profiles (1 halo term) + 2pt correlation (2 halo term).

(Ma 1998)

Nonlinear evolution of the power spectrum D(k)

Nonlinear growth

Linear power

Peacock (2002)Two halo term

One halo term

Nonlinear power spectrum D2(k) interpreted by the halo model

Power spectrum of the IR background from dusty galaxies

Takeuchi et al. (2005a)

Righi et al. (2008b)

Contribution of extragalactic CO lines to the foreground

Though CO lines do not contribute dominantly to the extragalactic IR background, they are substantially important in the Galactic foreground (e.g., Wright et al. 2001).

2.3 Theoretical development of IR galaxy evolution

Takeuchi et al. (2003, 2005b, 2010)

Now there are various SED models which can reproduce the observed galaxy SEDs very well. However, most of them are focused on reproducing the snapshot of the present-day SEDs, without dealing with the evolution.

What we need is a theoretical framework that can treat the evolution from a first principle (ab initio model).

To construct such a model, we must understand the complicated interaction of gas, dust and stars in galaxies. There are still only a few studies along this direction.

Infrared SED (unmixed, rSF=30pc, SFR=1.0Msunyr-1)

IR galaxy SED evolution model of a young galaxy

Takeuchi et al. (2005b)

Growth in ISMSN shock destruction

Dust evolution model in the chemical evolution framework

SFR

Gas

Metal

Dust

Metal production in stars

Hirashita (1999), Inoue (2003), Asano et al. (2010)

Dust evolution model in the chemical evolution framework

Asano et al. (2010)

The main contributor of dust switches from SNe to AGBs, and finally to the grain growth in the ISM. This is already incorporated in the SED model (Takeuchi et al. 2011).

3. Galactic Foregrounds3.1 Continuum components

Hinshaw et al. (2007)WMAP

Désert et al. (1990)

Classical dust model in the Galactic ISM

Radio

Condon (1992)

Synchrotron from supernova remnants ⇒ Related to star formation activity

Synchrotron

Dust

Free-free

M82

Radio wavelength: synchrotron and free-free emission

Synchrotron (simulated)

3.2 Effect of Galactic CO lines on CMB

CO (J = 1→0) map

The effect of CO rotational lines have very rarely discussed in the context of CMB foreground, but now we know that it is one of the most important ingredient (cf. Yamamoto-san and Aumont-san’s talks).

Schäfer et al. (2006)

HI-infrared correlation in the ISM

Boulanger et al. (1996)Based on IRAS-COBE.

3.3 Galactic foreground subtraction

Planck Collaboration (2011)

HI-infrared correlation in the ISM

There are three main categories of Galactic neutral hydrogen components: Local ISM, intermediate velocity clouds (IVCs), and high-velocity clouds (HVCs).

IVC: Galactic origin, Z ~ Z☉

HVC: extragalactic origin Z ~ 1/10 Z ☉

(e.g., Richter et al. 2001)

Signature of depletion is detected in HVCs ⇒ existence of dust!

However, There is no guarantee that they obey the same HI-to-dust relation with Galactic ISM.

Various neutral hydrogen components in the Galactic ISM

Various neutral hydrogen components in the Galactic ISM

Wakker et al. (2008)

Template construction for subtraction

A two-dimensional map-based point-to-point correlation is the standard method to make a template SED to subtract the Galactic foreground (cf. Hattori-san’s talk; Planck Collaboration 2011).

This is an endless chase: the better the angular-resolution of a map becomes, the finer ancillary data are requested (e.g., AKARI FIS all-sky diffuse map: Doi-san’s talk)! To ease this situation, state-of-the-art statistical methods are also introduced. But now, we also have to add CO lines to this process.

More physically-oriented approach will also help.

(⇔ power-spectrum approach for extragalactic background)

If a theoretical model can predict the statistical nature of the foreground of the ISM, it provides some information on the power spectrum Cℓ (without information of phase) rather than a map.

For example, some models of the power spectrum of the ISM fluctuation considering turbulence and magnetic field are proposed (Cho & Lazarian 2010; Fauvet et al. 2011; Hattori-san and Inutsuka-san’s talks).

Since it is tightly related to the alignment of dust grains, it is important for polarization studies.

3.4 Physico-statistical modeling of Galactic foreground

The SEDs of the foreground emission (dust continuum, synchrotron, free-free, and molecular lines) can be modeled in principle. In order to subtract the Galactic foreground, we have to estimate parameters for each component from the data. This was done in a point-to-point manner with ancillary datasets.

In the current situation, the parameter estimation will have practically infinite degrees of freedom.

Reasonable prior knowledge is necessary!

3.5 Incorporating evolutionary framework to the ISM

The extragalactic SED modeling technique, especially the evolutionary method would give a good prior as the first guess and integral constraint, since the sum of all components should reproduce a reasonable SED.

4. Summary and Prospects

1. The CMB foreground consists of Galactic and extragalactic components. The former is anisotropic, and the latter is isotropic.

2. The extragalactic foreground can be treated statistically, and the power-spectrum approach is powerful. This is dominated by dusty galaxies. To model this, we need accurate knowledge of the evolution of the SFR, SED, and clustering.

3. The Galactic foreground is anisotropic and structured, currently map-based method is the mainstream of the analysis. But in small scales, in addition to the point-to-point correlation, astrophysical approach is useful and should be developed.

4. Galaxy evolution approach may help even the Galactic foreground modeling and subtraction.

Acknowledgement

TTT has been supported by Program for Improvement of Research Environment for Young Researchers from Special Coordination Funds for Promoting Science and Technology commissioned by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.